This invention relates to a voltage generator circuit comprising a cell of the band-gap type, in which a plurality of m parallel-connected transistors form a compound first transistor of a first conductivity type, whose emitter is connected to one end of a first emitter resistor, the other end of this resistor being connected to the emitter of a second transistor of the same conductivity type whose emitter area is equal to that of one of the m transistors forming the compound first transistor, which second transistor has its base coupled to that of the first transistor, the node between the emitter of the second transistor and the first emitter resistor being coupled to a first supply terminal via a second emitter resistor, which circuit further comprises an amplifier acting upon the base of the first and of the second transistor to assure equality of the currents flowing through the first and the second transistor, respectively, the power supply to the collectors of these transistors being received from a second supply terminal.
A stabilized voltage generator is known particularly from the document EP-A-0,465,094.
Circuits for the generation of voltages which are independent of temperature and supply voltage variations are very often needed for the construction of modem integrated devices.
The principle of the circuit of the so-called band-gap type, which is based on a configuration of two transistors through which a similar current flows but which have an emitter-area ratio which differs from unity, thereby producing a difference in current density in these transistors and a correlated difference in emitter-base voltage, is now mainly used because of its excellent performance.
Mainly owing to some applications of battery-operated portable apparatuses the current trend is to specify that the corresponding circuits should be able to operate at a smaller supply voltage, particularly 3 V instead of 5 V, which used to be the customary standard. Some circuit arrangements then no longer perform satisfactorily and should be modified to allow operation at a low supply voltage.
Voltage generator circuits of the band-gap type generally require a supply voltage above 3 forward-biassed junction voltages (3.V.sub.BE) and even 4.V.sub.BE.
It is an object of the invention to provide a generator circuit of the band-gap type which can operate at a supply voltage slightly higher than the stabilised voltage generated by it (which is usually of the order of 2.V.sub.BE, i.e. .apprxeq.1.2 V), the stability of the circuit being at least as high as that of known circuits operating at a supply voltage of 5 V.